Regional and temporal relations of radon in soil gas to soil temperature and moisture

In deep soil where diffusional loss is negligible, the Rn concentration in soil gas is controlled by Ra, emanation coefficient (E), dry bulk density (ρb), and particle density (ρP), plus the transient properties of fraction water saturation (F) and temperature because the gaseous/aqueous partition coefficient for Rn (KT ) is temperature sensitive. In a typical soil (Ra = 30 Bq/kg, E = 0.2, ρb = 1.5 g/cm3, ρP = 2.65 g/cm3), Rn in soil gas (kBq/m3 ) is calculated to range from 21 (T = 0°C, F = 0.05) to 78 (T = 25°C, F = 0.95). At sites in Pennsylvania and elsewhere, measured soil gas Rn shows seasonal variations of 2‐ to 10‐fold. Much of this variability may be explained by temperature‐sensitive gaseous/aqueous partitioning. Since temporal soil moisture and temperature patterns vary geographically, temporal patterns in soil gas Rn vary geographically too. Mean soil gas Rn will tend to be higher in regions with warm or moist soils. Soil temperature and moisture are predictable from soil maps.